In the construction of roads and highways large drum mixers are often utilized to mix and heat asphalt aggregate mixtures for preparing the materials for application as a pavement. In addition, these drum mixers are often utilized in reconditioning applications where materials are removed from an existing roadway, heated and mixed with a conditioner, and then used to repave the roadway.
In the past, most of the drum mixers used for this purpose have been stationary installations requiring the materials to be transported to and from the installation. As pointed out in my copending application Ser. No. 747,295 entitled "Asphaltic Pavement Treating Apparatus and Method," there are numerous advantages in having the apparatus moved over the surface in a vehicular movement during which the materials are treated on a continuous basis. In that application there is shown a form of combination drum mixer and heating apparatus that is operated during vehicular movement wherein one or more burners emit an open flame for producing the hot gases. When an open flame is utilized, it is desirable to prevent the materials from directly contacting the flame, which because of its high temperature may cause the asphalt to flash and smoke, emitting pollutants into the atmosphere. In addition, it is also desirable to effect a uniform temperature distribution throughout the drum to prevent localized hot spots and uneven heating, which can also cause overheating and flashing of the asphalt.
For this reason in some drum mixers, such as the mixer disclosed in U.S. Pat. No. 3,845,941 to Mendenhall, the materials are tumbled over heated pipes which prevent direct exposure of the material to the flames and hot gases produced by the heating apparatus. Alternately, baffle plates or flame barriers, such as the barriers disclosed in U.S. Pat. No. 3,999,743 to Mendenhall, and in U.S. Pat. No. 4,039,171 to Shearer, may be mounted between the open flame and the interior of the drum to help prevent the material from directly contacting the open flame and to aid in the distribution of gases from the heating apparatus into the mixing drum.
Some of the problems with these prior art drum mixers is that the heating apparatus and flame barriers do not effectively distribute the hot gases through the mixing drum and/or are not sturdy enough to withstand the temperatures and the vibrations, jarring and impacts encountered during usage and transport as the apparatus is moved forwardly over the road or like supporting surface. In addition, some prior art flame barriers must be fabricated from expensive metals and materials in order to avoid warping and withstand the high temperatures present in the drum mixers.
Accordingly, it is an object of the present invention to provide simple, durable and relatively inexpensive heating apparatus for use in combination with drum mixers for producing hot gases and for uniformly distributing the gases into the drum mixer for heating materials.
Another object of the present invention is to provide heating apparatus for use in combination with drum mixers wherein an open flame is utilized for producing hot gases and the material to be heated is shielded from the open flame.
Yet another object of the present invention is to provide heating apparatus for use in combination with drum mixers, having a refractory lined combustion chamber and gas distributor plate constructed to withstand the impacts and high temperatures encountered in a drum mixer.